This invention relates to a valve and more particularly to a valve for controlling flow of fluid through an opening in an otherwise substantially fluid-tight barrier.
Granular dry materials, such as cat food and dried milk products, are frequently shipped in bags containing 10 pounds to 50 pounds of the dry material. The bags typically are made of, or have an interior lining of, a thermoplastic material such as polyethylene. The bags are filled and closed, e.g. by heat sealing, and are then palletized (placed in several layers to form a stack on a pallet) for transportation. Standard filling and sealing techniques do not allow removal of all the air from a bag that is filled with granular dry material during the filling and sealing operation. Accordingly, if the bag is made of fluid-tight material and is sealed in fluid-tight manner, a substantial quantity of air may be trapped inside the bag. This can cause a problem in palletizing the bags, because the bags that are lower in the stack on the pallet do not then support the bags that are higher in the stack in a firm and stable fashion. Consequently, it is common for a bag containing dry material to be perforated to allow air to escape when the bag is palletized even though it might appear to be fluid-tight. Although perforating the bag solves or mitigates the problem of air being trapped in the bag, this is not an ideal solution because it allows moisture and other contaminants to enter the bag, possibly causing spoilage of the contents.
It is known to package roasted coffee beans in a pouch provided with a valve that allows gas evolving from the coffee beans to escape from the pouch. A typical coffee valve is generally circular and includes a valve body, a cap and a diaphragm. The valve body has a generally flat valve seat or sealing surface that surrounds an opening and the diaphragm is positioned to lift from the sealing surface in the event that the pressure inside the coffee pouch exceeds the ambient pressure and to engage the sealing surface in the event that the ambient pressure exceeds the internal pressure in the coffee pouch.
In the conventional coffee valve, a film of silicone oil on the sealing surface fills gaps between the sealing surface and the diaphragm and thereby prevents leakage of air into the bag when the valve is closed. Surface tension of the silicone oil also tends to close the valve, and in fact when the valve opens under normal conditions, the diaphragm is forced away from the sealing surface over only a portion of the sealing surface and remains in contact with the sealing surface at other locations. Accordingly, when the pressure in the pouch drops sufficiently that flow of gas from the pouch stops, the surface tension of the silicone oil pulls the diaphragm back into contact with the sealing surface and restores the seal. The conventional coffee valve therefore provides an effective seal preventing entry of contaminants into the pouch, particularly when provided with silicone oil.
The rate at which gas evolves from roasted coffee beans is quite low and therefore the typical coffee valve need permit only a low flow rate to avoid excessive pressure build up in the pouch. However, the quantity of air trapped in a 50 pound bag of dog food may be such that it would take several hours for the air to escape through a standard coffee valve when the bag is placed at the bottom of a stack of similar bags on a pallet.
In addition, due to the nature of the process by which roasted coffee beans outgas, the rate at which gas evolves from the coffee beans does not undergo sudden changes, such that the pressure inside the pouch would increase rapidly unless the flow rate through the valve could increase rapidly. However, in the case of 10 to 50 pound bags of dry granular materials, when an upper bag is placed on top of a lower bag in a stack during palletizing, the pressure in the lower bag increases rapidly. If the lower bag were provided with a valve similar to the coffee valve but large enough to allow the air to escape in a few seconds or minutes, there is a high likelihood that the increase in pressure in the bag would displace the diaphragm from the sealing surface around its entire periphery, in which case the force of surface tension would no longer be available to pull the diaphragm back into contact with the sealing surface and closing of the valve could not be assured.
For the reasons set forth above, a valve based on the design and manner of operation of the conventional coffee valve is not suitable for venting a bag of granular dry material to prevent instability during palletizing.
In accordance with a first aspect of the present invention there is provided a valve for controlling flow of fluid through an aperture in a barrier, comprising a valve body including a pin and having a continuous sealing surface surrounding at least one opening through the valve body, and a diaphragm of resilient material, the diaphragm having a main surface and an opening surrounded by an inner margin, the diaphragm being disposed with the pin extending through said opening and with the main surface presented towards said sealing surface, and wherein the inner margin of the diaphragm is in a state of tension around the pin of the valve body, whereby the diaphragm is prestressed to a condition in which the main surface of the diaphragm engages the sealing surface of the valve body.
In accordance with a second aspect of the present invention there is provided, in combination, a bag including a barrier of substantially fluid-tight material, said barrier being formed with an aperture, and a valve for controlling flow of fluid through said aperture, the valve comprising a valve body secured to the barrier, the valve body including a pin and having a continuous sealing surface surrounding at least one passage through the valve body, and a diaphragm of resilient material, the diaphragm having a main surface and an opening surrounded by an inner margin, the diaphragm being disposed with the pin extending through said opening and with the main surface presented towards said sealing surface, and wherein the inner margin of the diaphragm is in a state of tension around the pin of the valve body, whereby the diaphragm is prestressed to a condition in which the main surface of the diaphragm engages the sealing surface of the valve body.